/***** BEGIN LICENSE BLOCK *****
 * Version: EPL 1.0/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Eclipse Public
 * License Version 1.0 (the "License"); you may not use this file
 * except in compliance with the License. You may obtain a copy of
 * the License at http://www.eclipse.org/legal/epl-v10.html
 *
 * Software distributed under the License is distributed on an "AS
 * IS" basis, WITHOUT WARRANTY OF ANY KIND, either express or
 * implied. See the License for the specific language governing
 * rights and limitations under the License.
 *
 * Copyright (C) 2010 Thomas E Enebo (tom.enebo@gmail.com)
 *
 * Alternatively, the contents of this file may be used under the terms of
 * either of the GNU General Public License Version 2 or later (the "GPL"),
 * or the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
 * in which case the provisions of the GPL or the LGPL are applicable instead
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package org.truffleruby.core.string;

import org.truffleruby.core.rope.Rope;
import org.truffleruby.parser.SafeDoubleParser;

public class DoubleConverter {
    private byte[] bytes;
    private int index;
    private int endIndex;
    private boolean isStrict;
    private char[] chars; // result string we use to parse.
    private int charsIndex;
    private int significantDigitsProcessed;
    private int adjustExponent;
    private boolean wroteExponent;
    private double result;

    // To match MRI so that we end up rounding on values greater than being storable in a 64
    // bit value in the same fashion we are using 30.  Based on wikipedia a note recommends
    //17 + 3 (or 20), but I don't know why that is recommended and we would rather be compatible
    //behaviorally with MRI.
    private final static int SIGNIFICANT_DIGITS_LIMIT = 30;
    // Maximal exponent is +308, minimal -308, -324 with subnormal float
    private final static int EXPONENT_DIGITS_LIMIT = 3;
    private final static int MAX_EXPONENT = (int) (Math.pow(10, EXPONENT_DIGITS_LIMIT)) - 1;
    // Max length is '-' + significant_digits + '.' + 'E' + '-' + exponent_digits
    // + 1 (first digit before point) + 1 (first decimal digit).
    private final static int MAX_LENGTH = SIGNIFICANT_DIGITS_LIMIT + EXPONENT_DIGITS_LIMIT + 6;

    public DoubleConverter() {
    }

    public void init(Rope rope, boolean isStrict) {
        bytes = rope.getBytes();
        index = 0;
        endIndex = index + rope.byteLength();
        this.isStrict = isStrict;
        // +2 for added exponent: E...
        // The algorithm trades digits for inc/dec exponent.
        // Worse case is adding E-1 when no exponent,
        // it trades one digit for 3 chars.
        chars = new char[Math.min(rope.byteLength() + 2, MAX_LENGTH)];
        charsIndex = 0;
        significantDigitsProcessed = 0;
        adjustExponent = 0;
        wroteExponent = false;
        result = -1.0; // -1.0 is "parse String"
    }

    private byte next() {
        return bytes[index++];
    }

    /**
     * Shift back to previous character in the incoming bytes
     *
     * @return false to indicate we are not in an EOS condition
     */
    private boolean previous() {
        index--;
        return false;
    }

    private boolean isEOS() {
        return index >= endIndex;
    }

    private boolean stopParsing() {
        index = endIndex;
        return true;
    }

    private boolean isDigit(byte b) {
        return b >= '0' && b <= '9';
    }

    private boolean isExponent(byte b) {
        return b == 'e' || b == 'E';
    }

    private boolean isWhitespace(byte b) {
        return b == ' ' || (b <= 13 && b >= 9 && b != 11);
    }

    private void addToResult(byte b) {
        chars[charsIndex++] = (char) b;
    }

    private void addExponentToResult(int exponent) {
        String exp = Integer.toString(exponent);
        for (int i = 0; i < exp.length(); i++) {
            addToResult((byte) exp.charAt(i));
        }
    }

    private boolean eatUnderscores() {
        while (!isEOS()) {
            byte value = next();

            if (value != '_') {
                previous();
                return isEOS();
            } else if (isStrict) {
                strictError();
            }
        }

        return true;
    }

    private double completeCalculation() {
        if (charsIndex == 0 || (charsIndex == 1 && chars[0] == '-')) { // "" or "-"
            strictError(); // Strict requires at least one digit.
            return 0.0; // Treated as 0.0 (not -0.0) in non-strict.
        } else if (isExponent((byte) chars[charsIndex - 1])) { // Covers 12.0efrog
            strictError();
            addExponentToResult(adjustExponent);
        } else if (isStrict && !isEOS()) {
            strictError(); // We know it is not whitespace at this point
        } else if (!wroteExponent && adjustExponent != 0) {
            addToResult((byte) 'E');
            addExponentToResult(adjustExponent);
        }

        return SafeDoubleParser.parseDouble(new String(chars, 0, charsIndex));
    }

    static class LightweightNumberFormatException extends NumberFormatException {
        private static final long serialVersionUID = 8405843059834590L;

        public LightweightNumberFormatException(String message) {
            super(message);
        }

        @SuppressWarnings("sync-override")
        @Override
        public Throwable fillInStackTrace() {
            return this;
        }
    }

    private boolean strictError() {
        if (isStrict) {
            throw new LightweightNumberFormatException("does not meet strict criteria");
        } else {
            return true; // means EOS for non-strict
        }
    }

    /**
     * Everything runs in 1.9+ mode now, so the `is19` parameter is vestigial.
     * However, in order to maintain binary compatibility with extensions we can't
     * just change the signature either.
     */
    public double parse(Rope rope, boolean strict, boolean is19) {
        init(rope, strict);

        if (skipWhitespace()) {
            return completeCalculation();
        }
        if (parseOptionalSign()) {
            return completeCalculation();
        }

        parseDigits();

        if (result != -1.0) { // abnormal result
            return result;
        }

        return completeCalculation();
    }

    /**
     * Consume initial whitespace and underscores so that next character
     * examined is not whitespace.  1.9 and strict do not allow leading
     * underscores.  Returns whether next position is at the end of the
     * string or not.
     * <p>
     * Trivia: " _ _ _ _ 1".to_f == 1.0 in Ruby 1.8
     */
    private boolean skipWhitespace() {
        while (!isEOS()) {
            byte value = next();

            if (isWhitespace(value)) {
                continue;
            }
            return previous();
        }

        return true;
    }

    private boolean parseOptionalSign() {
        byte sign = next();

        if (sign == '-') {
            addToResult(sign);
        } else if (sign != '+') {
            previous();  // backup...not a sign-char
        }

        return isEOS();
    }

    private boolean parseDigits() {
        if (!isEOS()) {
            byte value = next();

            if (isDigit(value)) {
                // Always add the first digit, in case it is the only digit
                if (value != '0') {
                    significantDigitsProcessed++;
                }
                addToResult(value);
            } else if (value == '.') {
                addToResult(value);
                return parseDecimalDigits();
            } else {
                return isEOS();
            }
        } else {
            strictError();
        }

        while (!isEOS()) {
            byte value = next();

            if (isDigit(value)) {
                if (significantDigitsProcessed < SIGNIFICANT_DIGITS_LIMIT) {
                    // Ignore leading 0s
                    if (value != '0' || significantDigitsProcessed > 0) {
                        significantDigitsProcessed++;
                        addToResult(value);
                    }
                } else {
                    adjustExponent++;
                }
            } else if (value == '.') {
                addToResult(value);
                return parseDecimalDigits();
            } else if (value == '_') {
                verifyNumberAfterUnderscore();
            } else if (isExponent(value)) {
                addToResult(value);
                return parseExponent();
            } else if (isWhitespace(value)) {
                return skipWhitespace();
            } else {
                return strictError();
            }

        }

        return true;
    }

    private boolean parseDecimalDigits() {
        if (isEOS()) {
            return strictError();
        }

        byte value = next();

        // Wonky, but 12._2e2 is 1200.0 and 12.__e2 is 12.0
        if (value == '_') {
            strictError();
            if (isEOS()) {
                return strictError();
            }
            value = next();
        }

        if (isDigit(value)) {
            if (significantDigitsProcessed < SIGNIFICANT_DIGITS_LIMIT) {
                if (!(value == '0' && significantDigitsProcessed == 0)) { // not a leading 0
                    significantDigitsProcessed++;
                }
            } else {
                value = '0';
            }
            // Always add a digit after the .
            addToResult(value);
        } else {
            return strictError();
        }

        while (!isEOS()) {
            value = next();

            if (isDigit(value)) {
                if (significantDigitsProcessed < SIGNIFICANT_DIGITS_LIMIT) {
                    if (value == '0' && significantDigitsProcessed == 0) { // leading 0
                        adjustExponent--;
                    } else {
                        significantDigitsProcessed++;
                        addToResult(value);
                    }
                } // otherwise ignore it
            } else if (isExponent(value)) {
                addToResult(value);
                return parseExponent();
            } else if (value == '_') {
                verifyNumberAfterUnderscore();
            } else if (isWhitespace(value)) {
                return skipWhitespace();
            } else {
                return strictError();
            }
        }

        return true;
    }

    private boolean parseExponent() {
        if (eatUnderscores()) {
            return isEOS();
        }

        byte value = next();

        int exponent = 0;
        int digits = 0;
        boolean negative = false;

        if (value == '-') {
            negative = true;
        } else if (value != '+') {
            previous(); // backup...not a sign-char
        }

        while (!isEOS()) {
            value = next();

            if (isDigit(value)) {
                if (digits < EXPONENT_DIGITS_LIMIT) {
                    // Ignore leading 0s
                    if (value != '0' || digits > 0) {
                        digits++;
                        exponent = 10 * exponent + (value - '0');
                    }
                } else {
                    return tooLargeExponent(chars[0] == '-', negative);
                }
            } else if (isWhitespace(value)) {
                skipWhitespace();
                break;
            } else if (value == '_') {
                verifyNumberAfterUnderscore();
            } else {
                strictError();
                stopParsing();
                break;
            }
        }

        if (negative) {
            exponent = -exponent;
        }

        exponent += adjustExponent;

        if (-MAX_EXPONENT <= exponent && exponent <= MAX_EXPONENT) {
            addExponentToResult(exponent);
            wroteExponent = true;
            return isEOS(); // Exponent end of double...let's finish.
        } else {
            return tooLargeExponent(chars[0] == '-', negative);
        }
    }

    private boolean tooLargeExponent(boolean negativeFloat, boolean negativeExponent) {
        if (negativeExponent) {
            if (negativeFloat) {
                result = -0.0;
            } else {
                result = 0.0;
            }
        } else {
            if (negativeFloat) {
                result = Double.NEGATIVE_INFINITY;
            } else {
                result = Double.POSITIVE_INFINITY;
            }
        }
        return stopParsing();
    }

    private void verifyNumberAfterUnderscore() {
        if (isStrict && (isEOS() || !isDigit(bytes[index]))) {
            strictError();
        }
    }
}
